Process for preparing (co)polychloroprene rubber

ABSTRACT

Process for preparing (co)polychloroprene rubber, comprising: 
     a first step (a) in which a portion of a polymerizable composition is partially polymerized according to a batchwise process, 
     a second step (b) in which the residual polymerizable composition is sequentially fed to the reaction mixture coming from the step (a), 
     a possible third step (c) in which the reaction mixture coming from the step (b) is polymerized up to the desired conversion rate.

This application is a continuation of application Ser. No. 08/529,155,filed Sep. 15, 1995.

The present invention relates to a process for preparing(co)polychloroprene rubber.

More specifically, the rubber according to the present invention isprepared by emulsion polymerizing a polymerizable compositionessentially constituted by chloroprene or a chloroprene mixture with oneor more copolymerizable monomers.

The classic way to prepare polychloroprene or copolychloroprenes inalkaline aqueous emulsion is well known in the art.

At present, most (co)polychloroprene rubbers are prepared by means of abatchwise process. This process, as well as the corresponding continuousprocess, are affected by some drawbacks, some of which are summarized asfollows.

A first drawback relates to safety and derives from the fact thatchloroprene is highly toxic and flammable and forms explosive mixtureswith air. As a consequence, particular attention must be paid especiallyto chloroprene polymerization initiation because at that point thechloroprene concentration inside the reactor is very high.

Another disadvantage which affects the process known in the prior art isthat copolymerizing chloroprene with other copolymerizable monomers,such as dienes, vinyl aromatic compounds, unsaturated acids, ester andnitrile derivatives of unsaturated carboxy acids, is very difficult.

Another drawback shown by the batchwise processes known in the priorart, is their reduced productivity.

The purpose of the present invention is provide a process for preparingrubbers by chloroprene polymerization or copolymerization, whichovercomes the drawbacks cited above.

For that purpose, the process according to the present invention iscarried out by emulsion polymerizing monomers essentially constituted bychloroprene or a mixture of chloroprene with one or more copolymerizablemonomers. This process is characterized in that:

a starting emulsion is formed which contains a fraction of monomers andfrom which the polymerization is started;

the reaction medium is fed together with the remaining amount of themonomers, and, possibly, with the balance of the other components whichconstitute the reaction medium;

the polymerization is allowed to continue until an overall conversionrate (TC) of the monomers to polymers is reached which is comprisedwithin the range of from 60 to 85%, preferably from 65 to 80%; and

essentially throughout the course of the polymerization an instant ratioof monomer:polymer (M:P), by weight, is maintained which is higher than,or equal to, about 0.20, preferably about 0.25, and still morepreferably, about 0.30.

This operating modality corresponds to a first preferred embodiment ofthe process according to the present invention.

According to a second embodiment of the invention, the following stepsare provided:

a first polymerization step (a) in which an aliquot (A) of monomers, byweight, is fed, and the polymerization is allowed to proceed until aconversion rate (CR) is reached which is comprised within the range offrom 3 to 80%, preferably of from 8 to 45%, and still more preferably offrom 10 to 30%;

and a second step (b) in which the reaction medium is fed together withat least the balance (B) of the monomers, by weight, is fed, with atleast the feed stream being controlled in such a way that the ratio ofM:P never becomes lower than the threshold values as defined hereinabovefor the first preferred embodiment.

According to such a preferred embodiment, the preliminary step (a) is awell distinct and time-limited sequence.

In the event when in the polymerization chloroprene and monomers of atleast one other type participate as monomers, the proportions of theseveral comonomers may have variable values:

in the starting reaction medium and in the feed stream first embodimentwithout (a) step!;

in the A fraction and in the B fraction second embodiment with (a)step!.

The selection of these proportions has a great influence on thepolymerization kinetics. This selection is perfectly within the skill ofthose skilled in the art.

According to an advantageous way of practicing the invention, the Afraction of (a) step represents from 1 to 50%, preferably from 3 to 25%,by weight, of the monomers.

Of course, the feed of the reaction medium with the B fraction can becarried out either batchwise or continuously. According to the presentinvention, in practice, continuous feed is the most frequently usedoperating way.

By varying the feed rate and therefore the amount of monomers added tothe reaction medium, the ratio of M:P can be controlled and adjusted.

The other components of the reaction medium are added eithersimultaneously with the monomers, or at a different time.

In general, the monomer feed is discontinued before the(co)polymerization reaches the maximum values as defined above for theconversion rate CR. However, also operating according to the oppositemodality falls within the scope of the invention.

Inasmuch as the feed of the monomers is discontinued before thethreshold values of CR are reached, one might consider that a last (c)step exists which corresponds to polymerization end, which follows the(b) step.

According to another variant of the invention, the starting reactionmedium also comprises (co)polymers and, preferably, polychloroprene.These constitute a kind of "seed" or "starter agent" constituted by akind of emulsion of polymers which may be either identical to, ordifferent from, the emulsion of (co)polymers which one wishes to obtain,it being understood that polychloroprene is particularly suitable forthis purpose, also in the case of (co)polymerization.

According to the present invention, the reaction medium should thereforebe preferably kept under conditions of slight monomer deprivation. Insuch a way, the ratio of M:P will be comprised within the range of from,e.g., 0.3 to 2.

The process according to the present invention can also be carried outinside one single reactor ("one pot process"); however, also a pluralityof reactors can be used as well.

The polymerization is carried out by means of the current polymerizationtechniques in alkaline aqueous emulsion, in the presence of one or moretranfer agent and one or more free radical initiators.

All emulsifiers and protecting colloids can be used in the processaccording to the present invention. From these agents, the water solublesalts, in particular sodium, potassium or ammonium salts, of thefollowing compounds can be cited: long-chain fatty acids, resin or gemresin derivatives, talloil, partially polymerized, isomerized ormodified resin; fatty alcohol sulfates, alkyl sulfates and alkylsulfonates; alkaline salts af alkylarylsulfonic acids as well as ofcondensation products of formol with aryl-sulfonic acids, as, e.g.,naphthalene-sulfonic acid; and ethylene oxide-phenol condensates.

The dispersing agent is preferably selected from the condensationproducts of formaldehyde with naphthalene-sulfonic acid or othersulfonates.

As free radical initiators, those compounds with peroxide character canbe mentioned in particular, as alkali-metal or ammonium persulfates,hydrogen peroxide, organic or mineral peroxides, such as cumeneperoxide, benzoyl peroxide, as well as alkali-metal and ammoniumferrocyanides, or some redox systems.

The transfer agent, or modifier agent, can be selected from iodoform,alkyl-xanthogen disulfides, alkyl mercaptans or still other sulfurbearing organic compounds.

The emulsion pH is preferably within the range of from about 11 to 13.

The polymerization is carried out under an inert atmosphere in theabsence of oxygen, with the temperature being within the range of from5° to 80° C., preferably from 10° to 50° C.

The monomers used in the practice of the process of the presentinvention essentially consist of either chloroprene alone or achloroprene mixture with one or more polymerizable (co)monomers.

The copolymerizable (co)monomers with chloroprene are vinyl-aromaticcompounds, e.g., styrene, vinyltoluenes, vinylnaphthalenes; unsaturatedmonocarboxy or dicarboxy acids, e.g., acrylic and methacrylic acid,itaconic acid, maleic acid, vinyl acetic acid, 2-(carboxy-methyl)acrylicacid; ester and nitrile derivatives of unsaturated carboxy acids, inparticular C₁ -C₆ -alkyl acrylates and methacrylates, acrylonitrile,methacrylonitrile; conjugated diolefins, e.g., 1,3-butadiene, isoprene,isobutadiene, 1-chlorobutadiene, 2,3-di-chlorobutadiene,2,3-dimethylbutadiene; vinyl eters, eters and ketones, e.g., vinylacetate, methylvinyl ether, methylvinyl ketone; sulfur.

According to a preferred embodiment, the monomers used are essentiallyconstituted by chloroprene or a mixture of chloroprene and1-chlorobutadiene, in which the 1-chlorobutadiene amount can constituteup to 50%, preferably up to 20%, by weight, of total monomers weight.

According to the process of the present invention, copolymers can beobtained which contain a level of comonomers, in particular1-chlorobutadiene, which is higher than as obtained, with the loadingbeing the same, with the batchwise process known from the prior art.

Furthermore, according to another aspect, the present invention alsorelates, as a novel industrial product, to a chloroprene copolymer withat least one other comonomer in which at least one of the othercomonomers is 1-chlorobutadiene, in which the latter can be present inan amount which is preferably lower than, or equal to, 50% by weightand, still more preferably, lower than or equal to 20% by weight, withreference to the total copolymer weight.

The invention also relates to a rubber composition based on this novelcopolymer.

In the first step (a) of the second preferred embodiment of the processaccording to the present invention, the reactor is charged with afraction A of the monomers which is comprised within the range of from 1to 50% by weight, preferably of from 3 to 25% by weight, based on totalmonomers amount. In this step (a), the monomers are polymerizedaccording to the batchwise process. In other terms, the reactor ischarged with a portion of the monomers, in such a way as to form thestarting emulsion with the usual additives (water, soap, dispersingagent). The concentration of monomers in the emulsion is generallycomprised within the range of from 30 to 70% by weight, based on totalemulsion weight.

The polymerization is carried out in the presence of free radicalinitiators and transfer agents.

In the first step (a) of the second embodiment of the process of thepresent invention, with said emulsion only 3-40%, preferably 10-30% oftotal reactor volume is filled.

The batchwise polymerization of the first step (a) is carried outaccording to a well known process, i.e., by adding the free radicalinitiator to the emulsion containing reactor and cooling said reactor inorder to keep it at the desired temperature level.

The conversion rate of the monomers at the end of the first step iscritical. This conversion rate should be comprised within the range offrom 3 to 80%, preferably of from 8 to 45%, still more preferably offrom 10 to 30%. Preferably, the high limit should not be exceeded. Infact, too high of a conversion rate can cause crosslinking to occur. Onthe contrary, too low of a conversion rate can cause a second populationto be formed during the course of the second step, and the reactionspeed to decrease.

The duration of the first step may vary as a function of the reactiontemperature and of monomer reactivity, and is usually comprised withinthe range of from 5 to 30 minutes, preferably of from 10 to 20 minutes.

The second step (b) of the second preferred embodiment of the processaccording to the present invention consists in progressively adding theresidual B monomer fraction. The free radical initiator, soap, water anddispersing agent must also be progressively added.

During the (b) step, the residual B fraction can be fed with an eitherconstant or variable feed rate, preferably with a constant feed rate.Should the reaction be very fast, the flow rate will be increased,should the reaction be slow, the flow rates will be decreased.

In order to prevent gel from being formed, and to obtain the desiredviscosity, the flow rates with which the residual B fraction, thecatalyst and soap are added to the reaction mixture (b) step! are veryimportant, These flow rates should be very well controlled, because itis important that in the reaction mixture a ratio of the residualmonomer(s) to the polymer (M:P) is always (and, above all, during thecourse of the feed) kept which is higher than or equal to 0.20,preferably higher than or equal to 0.25 and, still more preferably,higher than or equal to 0.30. In practice, the value of the M:P ratio iswithin the range of, e.g., from 0.30 to 2. A lower value of M:P ratiothan 0.20 may cause formation of gel to occur.

The duration of the (b) step may vary as a function of the reactiontemperature and of the reactivity of the polymerizable composition, andusually is comprised within the range of from 100 to 200 minutes and,preferably, of from 130 to 180 minutes.

The third step (c) according to the second preferred embodiment of theprocess according to the present invention consists of a possiblepolymerization step with controlled consumption of the residual portionof monomers until the desired conversion rate is reached, which shouldbe within the range of from 60 to 85%, preferably of from 65 to 80%.

The duration of the third step (c) depends on the desired conversionrate value and is usually within the range of from 30 to 100 minutes.

When the desired conversion rate is reached, the polymerization isdiscontinued by adding conventional polymerization inhibitors. It isalso possible to introduce, at polymerization interruption time, suchconventional antioxidant compounds as di-tert.butylparacresol,2,2'-methylene-bis(6-t-butyl-p-cresol),2,2'-thiobis-(4,6-di-t-butylphenol), 2,6-di-t-butyl-4-phenylphenol.

After the removal of monomer residues, and possible addition ofantioxidant compounds, the (co)polychloroprenic rubber can be recoveredaccording to any known modalities, for example, by precipitation causedby an electrolyte or by coagulation on a cold cylinder or a steam-heatedcylinder, washing and drying.

These (co)polychloroprenic rubbers have a storage stable Mooneyviscosity. They can be vulcanized by means of the conventionalvulcanization systems.

As compared to rubbers obtained according to the classic (eitherbatchwise or continuous) polymerization processes, the rubbers obtainedaccording to the process of the present invention display the advantagethat they can accept larger amounts of fillers such as, e.g., carbonblack, without thereby displaying any impairment of mechanicalproperties.

The process according to the present invention displays many otheradvantages:

(a) an increase in productivity:

the polymerization times are nearly identical, but when, e.g., thepolymerization is carried out batchwise in a reactor of 10 m³ capacity,at polymerization end there are approximately 9 m³ of latex; when thepolymerization is carried out according to the process of the presentinvention, 9.8 m³ of latex can be obtained with loading being the same;

(b) a higher safety:

according to the batchwise process, at reaction beginning there are,based on charged batch, approximately 50% of monomer: inside a reactorof 10 m³ of capacity there are 5 m³ of chloroprene; according to theprocess of the present invention, at polymerization beginning, the levelof monomer is of 20% at maximum, based on charged batch; therefore,inside a reactor of 10 m³ of capacity there will be an amount of atmaximum 0.7 m³ of chloroprene.

The following examples are reported for non-limitative purpose. In allexamples, the polymerization reaction is monitored by means of twomethodologies:

measurement of calories (instant measurement);

determination of conversion rate into solid species.

EXAMPLES Example No. 1

    ______________________________________                                        Reactor loading:                                                              ______________________________________                                        Chloroprene (CP) 8.70 parts*                                                  Mercaptan        0.02 parts*                                                  Deaerated softened water                                                                       61 parts*                                                    Modified rosin   0.52 parts*                                                  Sodium hydroxide 0.084 parts*                                                 ** Daxad 15      0.098 parts*                                                 ______________________________________                                         * parts per 100 parts of CP                                                   ** A watersoluble dispersing agent corresponding to the sodium salt of        naphthalene sulfonic acid condensed with formaldehyde.                   

The reaction medium is heated up to the desired polymerizationtemperature (42° C.) under a nitrogen atmosphere.

When that temperature is reached, the catalyst is fed: 2% (byweight/weight) sodium persulfate and 1% sodium hydrosulfite.

When the conversion has reached 15% (15 minutes), the aqueous andorganic phases and the catalyst (2% sodium persulfate and 1% sodiumhydrosulfite) are fed with a constant feed rate (b) step!.

    ______________________________________                                        Composition of aqueous phase:                                                 Softened water  19 parts*                                                     Modified rosin  2.09 parts*                                                   Sodium hydroxide                                                                              0.445 parts*                                                  "Daxad 15"      0.388 parts*                                                  Composition of organic phase:                                                 Chloroprene (CP)                                                                              91.3 parts*                                                   Mercaptan       0.235 parts*                                                  ______________________________________                                         *parts per 100 parts of CP                                               

The above solutions are fed during a time period of 150 minutes. At feedbeginning, the ratio of residual monomer to polymer, M:P, is ofapproximately 1.98; 30 minutes later, it is of 0.88; 60 minutes later itis of 0.62; 90 minutes later it is of 0.55; 120 minutes later it is of0.48 and 150 minutes later (end of continuous additions) it is of 0.42.At the end of the (b) step, the conversion rate of CP is of 60%.

The polymerization (c) step! is discontinued when a conversion rate CRof 75% is reached, by adding a chloroprene emulsion containing 0.01parts of t-butyl-catechol and 0.003 parts of phenothiazine.

The monomer residues are then removed by steam stripping, thenpolychloroprene is recovered by coagulating the latex, adjusted at a pHvalue of 6.5, on a cylinder kept cool at -20° C. The resulting film iswashed and then dried.

The resulting polymer has a Mooney viscosity (ML 1+4 at 100° C.) of 38.

Following Table 1 displays the aging behaviour of the resulting polymerand, for comparative purpose, the properties of both polymers, A1 andA2, as prepared at 40°-42° C. by means of the classic batchwise method.

                  TABLE 1                                                         ______________________________________                                                      Example    Comp. Ex.                                                                              Comp. Ex.                                   References    1          A1       A2                                          ______________________________________                                        ML 1 + 4 @ 100° C.,                                                    initial value 38         42       40                                          after 3 d @ 70° C.                                                                   +1         +4       +5                                          after 5 d @ 70° C.                                                                   +1         +4       +5                                          after 7 d @ 70° C.                                                                   +2         +5       +7                                          after 10 d @ 70° C.                                                                  +3         +7       +9                                          ______________________________________                                         * d = days at temperature noted                                          

One will observe that, as regards the aging properties, the polymerprepared according to the present invention displays bettercharacteristics than those prepared according to the classic batchwiseprocedure.

The properties of the vulcanizates (vulcanization carried out at 150° C.during 40 minutes) are displayed in Table 2. The initial properties arepractically identical; on the contrary, the properties measured afteraging demonstrate that the product prepared according to the presentinvention has a higher heat resistance.

                  TABLE 2                                                         ______________________________________                                                      Example    Comp. Ex.                                                                              Comp. Ex.                                   References    1          A1       A2                                          ______________________________________                                        Elongation, % 380        375      395                                         after 3 d @ 100° C.                                                                  375        350      365                                         after 21 d @ 100° C.                                                                 204        156      159                                         Tensile strength,                                                             MPa           17.5       18.2     18.9                                        after 3 d @ 100° C.                                                                  17.5       17.0     17.3                                        after 21 d @ 100° C.                                                                 14.7       11.6     13.6                                        ______________________________________                                         * d = days at temperature noted.                                         

Example No. 2

According to the process disclosed in Example No. 1, 4.35 parts/100parts of monomer are charged to the reactor (a) step!. Thepolymerization is carried out at 42° C.; the conversion rate CR of themonomer at the end of the first step (10 minutes) is of 16%. Theaddition of organic (95.65% of monomer+mercaptan) and aqueous (water,resin, Daxad 15, sodium hydroxide) phases and of catalyst is carried outduring 150 minutes (b) step!. At the beginning of the (b) step, theratio of residual monomer to polymer M:P is of about 1.30; after 30minutes it is of 1.0; after 60 minutes it is of 0.80; after 90 minutesit is of 0.72; after 120 minutes it is of 0.70; and after 150 minutes,it is of 0.65. At the end of (b) step, the conversion rate CR of monomeris of 55%. The reaction (c) step! is discontinued when the conversionrate reaches the value of 75%.

Total reaction time: 240 minutes.

The rubber displays a Mooney viscosity (ML 1+4 at 100° C.) of 47.

After 3-day aging at 70° C., the Mooney viscosity is of 48.

The so obtained rubber displays a different molecular weightdistribution (as determined by G.P.C.--Gel Permeation Chromatography)than as of polymers prepared according to the batchwise process:

    M.sub.w =419×10.sup.3, M.sub.n =131×10.sup.3, Ip (polymer polidispersity index)=3.20.

A rubber prepared according to the batchwise process (Mooneyviscosity=48) displays the following characteristics:

    M.sub.w =431×10.sup.3, Mn=160×10.sup.3, Ip=2.68.

The properties of raw and vulcanized compounds as a function of carbonblack level, expressed as phr (parts per hundred parts of rubber) arereported in following Table 3.

In said Table, also the properties are reported of (raw and vulcanized)compounds, as obtained from polymerized rubber according to thebatchwise process (A1). Mooney viscosity is ML 1+4 viscosity at 100° C.

Based on 100 parts of rubber, the raw compounds, besides variable levelsof carbon black, contain magnesium oxide (4 parts), stearic acid (0.5part), aromatic oil (5 parts), zinc oxide (5 parts), ethylene-thiourea(0.5 part).

                  TABLE 3                                                         ______________________________________                                        POLYMERS EXAMPLE No. 2   A1                                                   ______________________________________                                        CARBON   30     35     40   45   30   35   40   45                            BLACK (SRF)                                                                   Mooney   46     51     54   58   58   60   66   72                            VULCANIZA-                                                                    TION AT 120°                                                           C. (MN. S)                                                                    MIN      22     24     26   28   27   27   30   33                            +3       10     8.5    8    7.5  9    8    7.5  7                             +10      15     13.5   12.5 12   13.5 12   12.5 12                            +20      20.5   19     18   17.5 18.5 16.5 17.5 16                            +30      27.5   28     24.5 22   22   21   21   19                            MONSANTO                                                                      160° C. angle                                                          of 1° (MN.S)                                                           MAX      38     41     43   46   41   44   46   50                            MIN      5      6      6    6    6    7    7.5  8.5                           +2       2.75   3      2.75 2.5  2.5  2.5  2.75 2.5                           +10      5      4.75   4.5  4.25 3.75 4.5  4.75 4.25                          +30      19     14.2   12   12.2 17   13   11.7 10                            ______________________________________                                    

The rubbers obtained by means of the present invention allow morediluted compounds to be prepared, i.e., advantageous from a practicaloperating viewpoint, with the properties remaining anyway constant.

The above makes it possible cheaper compounds to be obtained, howeverhaving good mechanical properties.

For instance, Example No. 2 with 45 parts of carbon black has the sameMooney viscosity value (as determined on the compound) as of Example A1with 30 parts of carbon black, with both neat rubbers having practicallysame Mooney viscosity values (as measured on the rubber) (38 and 42,respectively).

Example No. 3 Copolymerization of 1-Chlorobutadiene at 42° C.

In the (a) step, the reactor is charged with 2.5 parts/100 parts of1-chlorobutadiene (1-CBD) and 7.5 parts/100 parts of chloroprene (CP);in this first step, the conversion is of 20% (requires 15 minutes).

Residual chloroprene is continuously added during the second step (b),during the course of 150 minutes.

At the beginning of the step (b), the ratio of monomer residues tocopolymer (M/P) is of about 1.15; 30 minutes later, said ratio hasdecreased down to 1.09; 60 minutes later, it is of 1.02; 90 minuteslater, of 1.0; 120 minutes later, of 0.96; and 150 minute, later, it isof 0.85.

The overall conversion rate (CR) at the end of the (b) step is of 60%.

The reaction is discontinued end of (c) step! ate CR=75% (200 minutes).

The conversion rate of 1-CBD, as determined by G.C. (GasChromatography), is of 50%; overall conversion rate CR: 75%.

The rubber, obtained according to the same process as disclosed inExample No. 1, displays a Mooney viscosity (ML 1+4 at 100° C.), of 47.

After three-day aging at 70° C, Mooney viscosity is 52.

Comparison Example No. 4

A polymerization mixture consisting of 97.5% of CP and 2.5% of 1-CBD, ispolymerized at 42° C. according to the batchwise process, until a totalconversion rate CR of 75 is obtained. The conversion of 1-CBD only is of20%.

Example No. 5 Copolymerization of 1-Chlorobutadiene at 30° C.

Reactor charging with 1-CBD: 2.5 parts/100 parts during the (a) step;1.3 parts/100 parts during the (b) step.

Reactor charging with CP: 7.5 parts/100 parts during the (a) step, 88.7parts/100 parts during the (b) step.

Total conversion rate CR during the (a) step: 20% (15 minutes).

Conversion rate at (b) step end: 65% (150 minutes).

At (b) step beginning, the ratio of residual monomers to copolymer M:Pis of approximately 1.3; after 30 minutes, said ratio has decreased downto 1.0; after 60 minutes, it is of 0.86; after 90 minutes it is of 0.76;after 120 minutes, of 0.72, and, after 150 minutes, it has decreaseddown to 0.65.

Overall conversion rate CR (c) step, after 195 minutes!: 75%.

Conversion rate (CR) of 1-CBD at polymerization end: 50%.

Properties of rubber obtained according to the procedure of Example 1:

(a) Mooney (ML 1+4 at 100° C.): 37;

(b) Mooney after 3 days at 70° C.: 40;

(c) Crystallization time:

t₀.5 =2.6 hours; after 7 hours: 96% crystallization; after 24 hours: 98%crystallization;

(d) T_(g) : -38° C.

Example No. 6 Copolymerization of 1-Chlorobutadiene at 30° C.

According to the same process as disclosed in Example No. 1, 2.5(parts/100 parts) of CP and 7.5 (parts/100 parts) of 1-CBD, are chargedduring the (a) step. The total conversion rate CR at the end of thefirst step (15 minutes) is of 25%.

(b) step: addition, with constant flow rate, of the organic (90parts/100 parts of CP+mercaptan) and aqueous (water, resin, Daxad 15,sodium hydroxide) phases, during 150 minutes.

At (b) step beginning, the ratio of residual monomers to copolymer (M:C)is of about 1.2; 30 minutes later it has decreased down to 1.1; 60minutes later, it is of 0.90; 90 minutes later, 0.80; 120 minutes later,0.71; and after 150 minutes, it is of 0.65.

Conversion rate CR at (b) step end: 65%.

End conversion rate CR (after 210 minutes): 75%.

Conversion rate CR of 1-CBD: 50%.

The rubber, obtained according to the process disclosed in Example 1,shows the following characteristics:

(a) Mooney viscosity (ML 1+4 at 100° C.) equal to 48.

(b) T_(g) : -36.6° C.

(c) Crystallization time:

t₀.5 =8.2 hours; after 7 hours: 40% crystallization; after 24 hours: 66%crystallization.

Example No. 7 Copolymerization of 1-Chlorobutadiene at 55° C.

By operating according to the same process as disclosed in Example No.1, during the course of the (a) step, 2.4 (parts/100 parts) of 1-CBD and7.6 (parts/100 parts) of CP, are charged to the reactor. The totalconversion rate CR at the end of the first step (15 minutes) is of 25%

(b) step: addition, with a constant flow rate, of the organic (90parts/100 parts of CP+mercaptan) and aqueous (water, resin, Daxad 15,sodium hydroxide) phases, during the course of 150 minutes.

At the beginning of (b) step, the ratio of residual monomers tocopolymer M:P is of about 1.2; after 30 minutes, of 1.1.; after 60minutes, of 0.90; after 90 minutes, of 0.80; after 120 minutes, of 0.71and after 150 minutes, it is of 0.60.

End conversion rate (c) step, after 195 minutes!: 72%.

Conversion rate of 1-CBD: 45%.

The rubber, obtained according to the same process as disclosed inExample 1 hereinabove, displays the following characteristics:

(a) Mooney viscosity (ML 1+4 at 100° C.) equal to 49.

(b) Crystallization time:

t₀.5 =65 hours; after 7 hours: 19% crystallization; after 24 hours: 28%crystallization.

Examples Nos. 8 to 10

Tables 4-7 report the evaluation data of rubbers from Example Nos. 3,5-7, respectively.

Example No. 8

The properties of rubber from Example No. 3 are reported in Table 4, inwhich "ETU" means "ethylene thiourea" and MTBS means "benzothiazyldisulfide".

                  TABLE 4                                                         ______________________________________                                        FORMULA              8A     8B     8C   8D                                    ______________________________________                                        ZnO             parts    5      3    1    21                                  ETU             parts    0.5    0    0    0                                   MBTS            parts    0      0    0    2                                   Mooney viscosity of the                                                                       (MV4)           61.9                                          compound                                                                      Monsanto        max.     99.0   80.0 79.0 55.0                                153° C.  min.     13.0   13.0 14.0 12.0                                Angle 3° optimal  12.0   31.5 61.0 29.0                                Vulcanization   mln.     29.0   27.0 27.0 25.0                                120° C.  +3       8.0    >60  >60  >60                                                 +10      11.0   --   --   --                                  MECHANICAL PROPERTIES                                                         Elongation at break (%)                                                                       40 mn    363.0  460.0                                                                              545.0                                                                              665.0                               Tensile strength (MPa)                                                                        40 mn    20.7   22.4 21.0 21.9                                Modulus 100 (MPa)                                                                             40 mn    2.9    2.2  1.7  1.5                                 Modulus 200 (MPa)                                                                             40 mn    7.9    6.0  4.4  3.7                                 Modulus 300 (MPa)                                                                             40 mn    15.8   12.2 8.8  7.4                                 Hardness (PTS)  40 mn    61.5   57.0 52.0 48.0                                Crystallization, 12° C.                                                                24 hours 77%    89%  90%  79%                                 ______________________________________                                    

From this Table one will see that chloroprene/1-chlorobutadienecopolymers obtained according to the present invention can be vulcanizedwithout ETU.

According to the compound composition, vulcanization curves are obtainedwhich can be at all different.

The addition of ETU yields products tending to undergo scorching.

With ETU-free formulations mechanical properties are obtained which areat all correct.

Example No. 9

Table 5 reports the evaluation data of rubbers from Examples 5 and 6,and, for comparison purposes, of two homopolymers prepared at 42° C.(A1) and at 57° C. (A4).

                  TABLE 5                                                         ______________________________________                                        FORMULA              5      6      A1   A4                                    ______________________________________                                        ZnO             parts    5      5    5    5                                   ETU             parts    0.5    0.5  0.5  0.5                                 Mooney viscosity of neat rubber                                                                        37.0   40.0 46.0 41.0                                Mooney viscosity of the                                                                       (MV4)    62.0   55.1 72.0 65.0                                compound                                                                      Monsanto        max.     96.0   96.0 104.0                                                                              101.0                               153° C.  min.     13.0   14.0 16.0 14.5                                Angle 3° optimal  14.0   8.0  21.0 21.0                                Vulcanization   min.     29.0   25.0 33.0 33.0                                120° C.  +3       9.0    7.5  7.5  7.5                                                 +10      13.0   10.5 10.5 9.0                                 MECHANICAL PROPERTIES                                                         Elongation at break (%)                                                                       40 mn    413.0  362.0                                                                              427.0                                                                              360.0                               Tensile strength (MPa)                                                                        40 mn    23.2   18.0 23.7 19.9                                Modulus 100 (MPa)                                                                             40 mn    2.7    2.6  2.7  2.7                                 Modulus 200 (MPO)                                                                             40 mn    7.6    7.0  7.5  7.5                                 Modulus 300 (MPa)                                                                             40 mn    15.2   13.7 14.8 15.5                                Hardness (PTS)  40 mn    62.0   60.0 60.5 62.0                                Crystallization, 12° C.                                                                7 hours  97.0   19.0 94.0 39.0                                Crystallizalion, 12° C.                                                                24 hours 98.0   37.0 100.0                                                                              60.0                                ______________________________________                                    

One will observe that low-temperature polymerizations can be carried out(30° C.), even with slow crystallization rates.

By adjusting the polymerization temperature and the level of1-chlorobutadiene, rubbers are obtained with similar mechanicalproperties (Examples 6 and A4) and a slower crystallization rate.

Example No. 10

In following Table 6 the evaluation is reported of the rubber fromExample 7.

                  TABLE 6                                                         ______________________________________                                        FORMULA                 10A    10B    10D                                     ______________________________________                                        ZnO                parts    5      3    1                                     ETU                parts    0.5    0    0                                     MBTS               parts    0      0    2                                     Mooney viscosity of the compound                                                                 (MV4)    55.1   --   --                                    Monsanto           max.     96.0   90.0 63.0                                  153° C.     min.     14.0   14.0 14.0                                  Angle 3°    optimal  8.0    22.0 24.0                                  Vulcanization      min.     25.0   23.0 22.0                                  120° C.     +3       7.5    >60  >60                                                      +10      10.5   --   --                                    MECHANICAL PROPERTIES                                                         Elongation at break (%)                                                                          40 mn    362.0  406.0                                                                              568.0                                 Tensile strength (MPa)                                                                           40 mn    18.0   18.2 18.3                                  Modulus 100 (MPa)  40 mn    2.6    2.1  1.5                                   Modulus 200 (MPa)  40 mn    7.0    5.8  3.7                                   Modulus 300 (MPa)  40 mn    13.7   11.7 7.1                                   Hardness (PTS)     40 mn    60.0   56.5 50.0                                  Crystallization, 12° C.                                                                   7 hours  19     19   19                                    Crystallization, 12° C.                                                                   72 hours 53     53   53                                    ______________________________________                                    

The single accompanying figure displays vulcanization curves, for twocopolymer products with different levels of 1-CBD (Example Nos. 5 and 6)polymerized at 30° C. and, for comparative purposes, for a product (B)polymerized at approximately 70° C. according to the discontinuousprocess.

When 1-CBD is contained at a rather high level (Example No.6) ahigh-slope curve is obtained. By modifying the level of 1-CBD, thevulcanization speed decreases.

This property may prove to be interesting in order to increase theproductivity in fabrication facilities.

We claim:
 1. A process for preparing a (co)polymeric rubber ofpolychloroprene by emulsion polymerizing monomers, which monomerscomprise chloroprene, the process comprising:(a) forming an emulsionfrom which the polymerization is started, the emulsion comprising afraction of the monomers, the conversion rate of the monomers at the endof this step is in the range of from about 3 to 80%; (b) feeding theremaining monomers to the emulsion and allowing the polymerization toproceed; and (c) optionally continuing the polymerization until reachingan overall conversion rate of the monomers in the range of from about 60to 85%; wherein the monomer/polymer weight ratio during steps (a), (b),and (c) is maintained at about 0.20 or more, and wherein the emulsion pHis alkaline and in the range of from about 11 to
 13. 2. The processaccording to claim 1, wherein the step (c) polymerization is continueduntil the overall conversion rate of the monomers is in the range offrom about 65 to 80%.
 3. The process according to claim 1, wherein aweight ratio of monomer:polymer is maintained at about 0.25 or moreessentially throughout the polymerization.
 4. The process according toclaim 3, wherein the weight ratio of monomer:polymer is maintained atabout 0.3 or more essentially throughout the polymerization.
 5. Theprocess according to claim 4, wherein the weight ratio ofmonomer:polymer is maintained in the range of from about 0.3 to 2essentially throughout the polymerization.
 6. The process according toclaim 1, wherein the conversion rate of the monomers at the end of step(a) is in the range of from about 8 to 45%.
 7. The process according toclaim 6, wherein the conversion rate of the monomers at the end of step(a) is in the range of from about 10 to 30%.
 8. The process according toclaim 1, wherein the fraction of the monomers is about 1 to 50% byweight based on the total weight of monomers.
 9. The process accordingto claim 8, wherein the fraction of the monomers is about 3 to 25% byweight based on the total weight of monomers.
 10. The process accordingto claim 1, wherein the monomers consist essentially of chloroprene. 11.The process according to claim 1, wherein the monomers comprise amixture of chloroprene and 1-chlorobutadiene, wherein the1-chlorobutadiene is present in an amount up to 50% by weight of thetotal weight of monomers.
 12. The process according to claim 11, whereinthe amount of 1-chlorobutadiene is present in an amount up to 20% byweight of the total weight of monomers.
 13. A process for preparing a(co)polymeric rubber of polychloroprene by emulsion polymerizingmonomers, which monomers comprise chloroprene, the processcomprising:(a) forming an emulsion from which the polymerization isstarted, the emulsion comprising a fraction of the monomers, theconversion rate of the monomers at the end of this step is in the rangeof from about 3 to 80%; (b) feeding the remaining monomers to theemulsion and allowing the polymerization to proceed; and (c) optionallycontinuing the polymerization until reaching an overall conversion rateof the monomers in the range of from about 60 to 85%; wherein themonomer/polymer weight ratio during steps (a), (b), and (c) ismaintained at about 0.20 or more, and wherein the emulsionpolymerization is carried out in the presence of a protective colloid.14. The process according to claim 13, wherein the step (c)polymerization is continued until the overall conversion rate of themonomers is in the range of from about 65 to 80%.
 15. The processaccording to claim 13, wherein a weight ratio of monomer:polymer ismaintained at about 0.25 or more essentially throughout thepolymerization.
 16. The process according to claim 15, wherein theweight ratio of monomer:polymer is maintained in the range of from about0.3 to 2 essentially throughout the polymerization.
 17. The processaccording to claim 13, wherein the conversion rate of the monomers atthe end of step (a) is in the range of from about 8 to 45%.
 18. Theprocess according to claim 13, wherein the fraction of the monomers isabout 1 to 50% by weight based on the total weight of monomers.
 19. Theprocess according to claim 13, wherein the monomers consist essentiallyof chloroprene.
 20. The process according to claim 13, wherein themonomers comprise a mixture of chloroprene and 1-chlorobutadiene,wherein the 1-chlorobutadiene is present in an amount up to 50% byweight of the total weight of monomers.